U.S. patent application number 12/926844 was filed with the patent office on 2011-12-29 for lithium manganese oxide-carbon nano composite and method for manufacturing the same.
This patent application is currently assigned to INDUSTRY-ACADEMIC COOPERATION FOUNDATION, YONSEI UNIVERSITY. Invention is credited to Dong Hyeok Choi, Hye Ryun Choi, Hyun Chul Jung, Hak Kwan Kim, Kwang Bum Kim, Sang Bok Ma.
Application Number | 20110318639 12/926844 |
Document ID | / |
Family ID | 45352848 |
Filed Date | 2011-12-29 |
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United States Patent
Application |
20110318639 |
Kind Code |
A1 |
Kim; Hak Kwan ; et
al. |
December 29, 2011 |
Lithium manganese oxide-carbon nano composite and method for
manufacturing the same
Abstract
There is provided a method for manufacturing a lithium manganese
oxide-carbon nano composite by mixing a lithium ion solution with a
manganese ion solution, dispersing a carbon material in the
solution in which the lithium ion is mixed with the manganese ion,
and forming the lithium manganese oxide on a surface of the carbon
material by maintaining the solution in which the carbon material
is dispersed at a predetermined temperature. In addition, there is
provided the lithium manganese oxide-carbon nano composite formed
by coating the carbon material with the lithium manganese oxide at
a thickness of several nm. There is provided a manufacturing
apparatus capable of coating the carbon material with the lithium
manganese oxide at a thickness of several nm.
Inventors: |
Kim; Hak Kwan; (Hanam,
KR) ; Jung; Hyun Chul; (Yongin, KR) ; Choi;
Dong Hyeok; (Suwon, KR) ; Kim; Kwang Bum;
(Seoul, KR) ; Ma; Sang Bok; (Seoul, KR) ;
Choi; Hye Ryun; (Seoul, KR) |
Assignee: |
INDUSTRY-ACADEMIC COOPERATION
FOUNDATION, YONSEI UNIVERSITY
Seoul
KR
SAMSUNG ELECTRO-MECHANICS CO., LTD.
Suwon
KR
|
Family ID: |
45352848 |
Appl. No.: |
12/926844 |
Filed: |
December 13, 2010 |
Current U.S.
Class: |
429/224 ;
252/182.1; 422/109; 977/742 |
Current CPC
Class: |
H01G 11/30 20130101;
H01G 11/50 20130101; Y02T 10/70 20130101; B82Y 30/00 20130101; Y02E
60/10 20130101; Y02E 60/13 20130101; C01P 2004/80 20130101; H01M
4/505 20130101; B82Y 40/00 20130101; H01M 4/1391 20130101; H01M
4/587 20130101; C01B 32/168 20170801; H01M 4/366 20130101; C01G
45/1242 20130101 |
Class at
Publication: |
429/224 ;
252/182.1; 422/109; 977/742 |
International
Class: |
H01M 4/505 20100101
H01M004/505; G05D 23/00 20060101 G05D023/00; H01M 4/88 20060101
H01M004/88 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2010 |
KR |
10-2010-0060149 |
Claims
1. A method for manufacturing a lithium manganese oxide-carbon nano
composite, comprising: mixing a lithium ion solution with a
manganese ion solution; dispersing a carbon material in the
solution in which the lithium ion is mixed with the manganese ion;
and synthesizing lithium manganese oxide on a surface of the
dispersed carbon material.
2. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, wherein the synthesizing of the lithium
manganese oxide supplies heat in order to maintain a predetermined
temperature.
3. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, further comprising controlling at least
one of the amount of lithium, the amount of manganese, the amount
of carbon material, a reaction time, and a reaction temperature in
order to control any one of the thickness of the lithium manganese
oxide, the synthesis amount of the lithium manganese oxide and the
ratio of lithium to manganese of the lithium manganese oxide.
4. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, further comprising controlling anyone of
the temperature and pressure during the synthesis in order to
control the synthesis of the lithium manganese oxide.
5. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, wherein the carbon material is any one
of carbon black, a carbon nano tube (CNT), a carbon nano fiber
(CNF), a vapor grown carbon fiber (VGCF), graphite, and
grephene.
6. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, wherein the lithium ion is a
mono-valence lithium ion.
7. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, wherein the lithium ion solution is any
one of LiOH, LiNO.sub.3 and LiCl.
8. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, wherein the manganese ion is a 7-valence
manganese ion.
9. The method for manufacturing a lithium manganese oxide-carbon
nano composite of claim 1, wherein the manganese ion solution is
any one of KMnO.sub.4 and NaMnO.sub.4.
10. A lithium manganese oxide-carbon nano composite for
manufacturing an electrode for a high-output energy storage device,
comprising: a carbon material: and a nano-sized lithium manganese
oxide formed on the surface of the carbon material.
11. The lithium manganese oxide-carbon nano composite for
manufacturing an electrode for a high-output energy storage device
of claim 10, wherein the lithium manganese oxide formed in the
carbon material has a size of 10 nm or less.
12. The lithium manganese oxide-carbon nano composite for
manufacturing an electrode for a high-output energy storage device
of claim 10, wherein the lithium manganese oxide formed in the
carbon material has a lithium manganese oxide-spinel structure.
13. The lithium manganese oxide-carbon nano composite for
manufacturing an electrode for a high-output energy storage device
of claim 10, wherein the carbon material is any one of carbon
black, a carbon nano tube (CNT), a carbon nano fiber (CNF), a vapor
grown carbon fiber (VGCF), graphite, and grephene.
14. The lithium manganese oxide-carbon nano composite for
manufacturing an electrode for a high-output energy storage device
of claim 10, wherein the lithium manganese oxide is
LiMn.sub.2O.sub.4.
15. An apparatus for manufacturing a lithium manganese oxide-carbon
nano composite, comprising: an airtight chamber receiving a lithium
ion solution and a manganese ion solution and synthesizing a
lithium manganese oxide with a carbon nano composite; a heat supply
unit supplying heat to the airtight chamber; a temperature-pressure
measuring unit measuring at least one of temperature and pressure
in the airtight in order to control heat supplied to the heat
supply unit; and a temperature-pressure control unit controlling at
least one of temperature and pressure according to the measured
temperature and pressure.
16. The apparatus for manufacturing a lithium manganese
oxide-carbon nano composite of claim 15, wherein the heat supply
unit is a microwave scanning apparatus.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of Korean Patent
Application No. 10-2010-0060149 filed on Jun. 24, 2010, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a carbon nano composite for
manufacturing a high-output energy storage device and a method for
manufacturing the same, and more particularly, to a lithium
manganese oxide-carbon nano composite and a method for
manufacturing the same.
[0004] 2. Description of the Related Art
[0005] Generally, an electrochemical energy storage device, which
is a core component that is essential for use in finished products
such as portable information communications devices, and other
electronic devices, has recently gathered attention as a
high-quality energy storage device within the field of renewable
energy, such as for a future electric car, storing wind power,
solar energy, or the like.
[0006] An electrochemical capacitor as a currently developed
new-generation energy storage system is a high-output energy
storage device that has excellent characteristics in terms of
energy density as compared to a dielectric capacitor and excellent
characteristics in terms of output density as compared to a
rechargeable battery. Therefore, the electrochemical capacitor has
been used as a power supply for driving portable electronic
communications devices, an electric car, a hybrid car, or the like,
that demand high energy output within a short period of time.
[0007] A representative energy storage system using an
electrochemical principle may include a lithium ion battery and an
electrochemical capacitor. Recently, the electrochemical capacitor
has been developed to maximize the capacity of a high-output
capacitor, so as to improve the output characteristics of a
high-capacity lithium rechargeable battery.
[0008] The lithium rechargeable battery is a battery that can be
consecutively recharged using lithium ions. The lithium
rechargeable battery is excellent in terms of the amount of energy
(energy density) that can be stored per unit weight or volume, but
has degraded efficiency in terms of service lifespan, charging
time, and amount of energy (output density) usable per unit
time.
[0009] The electrochemical capacitor is classified into an
electrochemical double layer capacitor (EDLC) using an
electrochemical double layer phenomenon at an electrode-electrolyte
interface and a pseudo capacitor having high capacitance by a
reversible faraday oxidation-reduction reaction at the
electrode-electrolyte interface.
[0010] An example of a metal oxide for a cathode of a lithium
rechargeable battery may include LiCoO.sub.2, LiMn.sub.2O.sub.4,
LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2, LiFePO.sub.4, or the like.
Among others, LiCoO.sub.2 has been mainly used. However, research
into LiMn.sub.2O.sub.4 has been conducted in order to replace
expensive Co and improve output characteristics.
[0011] An example of the electrode material of the pseudo capacitor
may include a metal oxide-based conductive polymer, or the like. In
particular, RuO.sub.2, among transition metal oxides used as a
pseudo capacitor electrode material, has very high specific
capacitance, long operating time, high electric conductivity, and
excellent high-rate capability in an aqueous electrolyte.
[0012] RuO.sub.2 has the above-mentioned excellent characteristics
but is expensive. As a result, efforts to replace RuO.sub.2 have
been actively conducted. High-capacity and inexpensive
LiMn.sub.2O.sub.4 has been developed as a replaceable electrode
material. As a method for manufacturing LiMn.sub.2O.sub.4, a method
for mixing a lithium salt and a manganese salt into a solid-phase
powder and performing a high-temperature heat treatment (at a
temperature of 500.degree. C. or more) thereupon has been most
frequently used. The solid-phase powder has been manufactured into
a powder state having an .mu.m size. In order to maximize the
electrochemical utility of the metal oxide, the development of
lithium manganese oxide having a nano size has been undertaken.
SUMMARY OF THE INVENTION
[0013] An aspect of the present invention provides a lithium
manganese oxide-carbon nano composite for manufacturing an
electrode having high energy density and high output
characteristics and a method for manufacturing the same.
[0014] According to an aspect of the present invention, there is
provided a method for manufacturing a lithium manganese
oxide-carbon nano composite by mixing a lithium ion solution with a
manganese ion solution, dispersing a carbon material in the
solution in which the lithium ion is mixed with the manganese ion,
and forming the lithium manganese oxide on a surface of the
dispersed carbon material by maintaining the solution in which the
carbon material is dispersed at a predetermined temperature.
[0015] The carbon material may be any one of carbon black, a carbon
nano tube (CNT), a carbon nano fiber (CNF), a vapor grown carbon
fiber (VGCF), graphite, and grephene.
[0016] The lithium ion may be a mono-valence lithium ion and the
lithium ion solution may be any one of LiOH, LiNO.sub.3 and
LiCl.
[0017] The manganese ion may be a 7-valence manganese ion and the
manganese ion solution may be any one of KMnO.sub.4 and
NaMnO.sub.4.
[0018] The method for manufacturing a lithium manganese
oxide-carbon nano composite may further include controlling at
least one of the amount of lithium, the amount of manganese, the
amount of carbon material, a reaction time, and a synthesis
temperature in order to control any one of a coated thickness and a
coated amount of the lithium manganese oxide and a ratio of lithium
to manganese of the lithium manganese oxide.
[0019] The method for manufacturing a lithium manganese
oxide-carbon nano composite further may include controlling at
least one of the temperature and pressure during the coating in
order to control the coating of the lithium manganese oxide.
[0020] According to another aspect of the present invention, there
is provided a lithium manganese oxide-carbon nano composite
including: a carbon material and a nano-sized lithium manganese
oxide formed on the surface of the carbon material.
[0021] The lithium manganese oxide formed in the carbon material
may have a size of 10 nm or less.
[0022] The lithium manganese oxide formed in the carbon material
has a lithium manganese oxide-spinel structure.
[0023] The carbon material may be any one of carbon black, a carbon
nano tube (CNT), a carbon nano fiber (CNF), a vapor grown carbon
fiber (VGCF), graphite, and grephene.
[0024] The lithium manganese oxide may be LiMn.sub.2O.sub.4.
[0025] According to another aspect of the present invention, there
is provided an apparatus for manufacturing a lithium manganese
oxide-carbon nano composite, including: an airtight chamber
receiving a lithium ion solution and a manganese ion solution and
synthesizing a lithium manganese oxide with a carbon nano
composite; a heat supply unit supplying heat to the airtight
chamber; a temperature-pressure measuring unit measuring at least
one of temperature and pressure in the airtight chamber in order to
control heat supplied to the heat supply unit; and a
temperature-pressure control unit controlling at least one of
temperature and pressure according to the measured temperature and
pressure.
[0026] The heat supply unit may be a microwave scanning
apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The above and other aspects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0028] FIG. 1 is a flowchart showing a method for manufacturing a
lithium manganese oxide-carbon nano composite according to the
present invention;
[0029] FIG. 2 is a graph showing absorbance according to a waveform
of a synthesis solution before and after the manganese ion solution
according to the present invention is heat-treated in the
water;
[0030] FIG. 3 is a graph showing a cyclic voltammogram after and
before the lithium manganese oxide-carbon nano composite according
to the present invention is heat-treated in the water;
[0031] FIG. 4 is a graph showing a constant current charge and
discharge profile before and after the lithium manganese
oxide-carbon nano composite according to the present invention is
heat-treated in the water;
[0032] FIG. 5 is a graph showing a discharge curve for each C-rate
of the lithium manganese oxide-carbon nano composite according to
the present invention;
[0033] FIG. 6 is a graph showing a C-rate dependency of specific
capacitance of the lithium manganese oxide-carbon nano composite
according to the present invention; and
[0034] FIG. 7 is a flowchart showing life characteristics of a
lithium manganese oxide-carbon nano composite according to the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] Hereinafter, exemplary embodiments will be described in
detail with reference to the accompanying drawings so that they can
be easily practiced by those skilled in the art to which the
present invention pertains. However, in describing the exemplary
embodiments of the present invention, detailed descriptions of
well-known functions or constructions are omitted so as not to
obscure the description of the present invention with unnecessary
detail.
[0036] In addition, like reference numerals denote parts performing
similar functions and actions throughout the drawings.
[0037] It will be understood that when an element is referred to as
being "connected with" another element, it can be directly
connected with the other element or may be indirectly connected
with the other element with element(s) interposed therebetween.
Unless explicitly described to the contrary, the word "comprise"
and variations such as "comprises" or "comprising," will be
understood to imply the inclusion of stated elements but not the
exclusion of any other elements.
[0038] Hereinafter, a carbon nano composite coated with a lithium
manganese oxide and a method for manufacturing the same according
to the present invention will be described with reference to FIG.
1.
[0039] FIG. 1 is a flowchart explaining a method for manufacturing
a lithium manganese oxide-carbon nano composite according to the
present invention.
[0040] A method for manufacturing a lithium manganese oxide-carbon
nano composite according to the present invention includes mixing a
lithium ion solution with a manganese ion solution (S10),
dispersing a carbon material in the solution in which the lithium
ion and the manganese ion are mixed (S20), and coating the surface
of the carbon material with the lithium manganese oxide by
maintaining the solution in which the carbon material is dispersed
at a predetermined temperature (S30).
[0041] Each step will now be described in more detail.
[0042] In order to manufacture the lithium manganese oxide-carbon
nano composite, the lithium ion solution and the manganese ion
solution are mixed with each other (S10).
[0043] A lithium mono-valence solution is used as a lithium ion
solution. The lithium ion is not limited thereto, but LiOH,
LiNO.sub.3, LiCl, or the like may be used. In addition, a manganese
7-valence solution is used as the manganese ion solution. The
manganese ion solution is not limited thereto, but KMnO.sub.4 or
NaMnO.sub.4, or the like, may be used.
[0044] The manganese 7-valence ion is mixed with the lithium
mono-valence ion by mixing the lithium ion with the manganese
ion.
[0045] The carbon material is dispersed in a solution in which the
lithium ion and the manganese ion are mixed (S20). An example of
the carbon material may include carbon black, a carbon nano tube
(CNT), a carbon nano fiber (CNF), a vapor grown carbon fiber
(VGCF), graphite, grephene, or the like, but is not limited
thereto.
[0046] According to the present invention, the carbon material may
be dispersed without using a separate oxidizer or reducer or
supplying electrical energy by dispersing the carbon material in
the solution in which the lithium mono-valence ion and the
manganese 7-valence ion are mixed, in order to disperse the carbon
material (hereinafter, `carbon nano tube` will be used herein to
describe the carbon material).
[0047] After dispersing the carbon nano-tube, the lithium manganese
oxide-carbon nano composite is manufactured through a step (S30) of
coating the surface of the carbon material with the lithium
manganese oxide by maintaining the solution, in which the carbon
nano tube is dispersed, at a predetermined temperature.
[0048] The process of forming LiMn.sub.2O.sub.4 by adding the
carbon nano composite to the mixing solution of the lithium ion
solution and the manganese ion solution may be described by the
following reaction formula.
MnO.sup.4-+4H.sup.++3e.sup.-.fwdarw.MnO.sub.2+2H.sub.2O
MnO.sub.2+2H.sub.2O.fwdarw.Mn.sup.4++4OH.sup.-
8Mn.sup.4++4Li.sup.++36OH.sup.-.fwdarw.4LiMn.sub.2O.sub.4+18H.sub.2O+O.s-
ub.2
[0049] The reaction is made by supplying heat. The carbon nano
composite serves as a reducing modifier and a substrate.
[0050] A permanganate ion is reduced into MnO.sub.2 on the carbon
nano composite by supplying heat and the reduced MnO.sub.2 exists
in a Mn +4-valence ion state through a hydrolysis reaction. The Mn
+4-valence ion is reduced into LiMn.sub.2O.sub.4 by LiOH and is
distributed to be educed on the carbon nano composite.
[0051] The reaction, which is an endothermic reaction, requires the
supply of heat. The present invention may supply heat through a
microwave hydrothermal process.
[0052] The exemplary embodiment of the present invention provides
an apparatus for manufacturing the lithium manganese oxide-carbon
nano composite, including an airtight chamber, a heat supply unit,
a temperature-pressure measuring unit, and a temperature-pressure
control unit.
[0053] In order to coat the carbon nano tube with the lithium
manganese oxide, the solution in which the manganese 7-valence ion
and the lithium mono-valence ion are mixed is put into the airtight
chamber. The carbon material put into the airtight chamber is
dipped into the mixing solution. The carbon material may be
dispersed without supplying the separate oxidizer or reducer or the
separate electrical energy (S20).
[0054] The apparatus for manufacturing the lithium manganese
oxide-carbon nano composite includes the heat supply unit. The heat
supply unit may use a microwave scanning apparatus that heats the
solution in the airtight chamber with microwave scanning apparatus.
The temperature of the mixing solution in the airtight chamber
rises due to the microwave scanning apparatus. The temperature in
the chamber can rapidly and uniformly rise due to the microwave
scanning apparatus.
[0055] Thereafter, the temperature is maintained constantly in
order to induce the coating of the carbon material with the lithium
manganese oxide. In order to maintain the predetermined
temperature, the apparatus for manufacturing the lithium manganese
oxide-carbon nano composite may include the temperature-pressure
measuring unit that can measure the temperature and/or pressure in
the chamber. In order to maintain the preset temperature according
to the measured temperature and/or pressure data values, the
apparatus for manufacturing the lithium manganese oxide-carbon nano
composite may include the temperature-pressure control unit that
controls the temperature in the chamber.
[0056] The temperature in the chamber may be constantly maintained
by using the temperature-pressure measuring unit and the
temperature-pressure control unit and may induce the coating of the
carbon material with the lithium manganese oxide (S30).
[0057] According to the exemplary embodiment of the present
invention, at least one of the amount of lithium, the amount of
manganese, the amount of carbon material, the reaction time, and
the synthesis temperature can be controlled in order to control the
coating amount and the coating thickness of the lithium manganese
oxide and the ratio of lithium to manganese in the lithium
manganese oxide.
[0058] The amount of lithium ion solution may be controlled in
order to control the amount of lithium, and the amount of lithium
ion solution may be controlled in order to control the amount of
manganese. The ratio of lithium to manganese in the lithium
manganese oxide can be controlled in the above-mentioned
manner.
[0059] Further, in order to control the coating amount and the
coating thickness of the lithium manganese oxide, the coating rate
can be controlled by controlling at least one of the amount of
lithium ion, the amount of manganese, and the amount of carbon
material within the mixing solution and the coating amount and the
coating thickness of the lithium manganese oxide can be controlled
by controlling the reaction time or the synthesis temperature.
[0060] The lithium manganese oxide-carbon nano composite according
to the present invention may perform the coating by the simple
process without using the oxidizer or reducer or supplying the
separate electrical energy. In addition, most of the carbon
material including the lithium manganese oxide formed at the nm
thickness may contribute to the specific capacitance even in the
high-output conditions, such that the electrochemical utility of
the lithium manganese oxide is increased and the electric
conductivity is improved.
[0061] The lithium manganese oxide is coated on the carbon nano
tube. In the case of the lithium manganese oxide-carbon nano
composite manufactured by the manufacturing method according to the
present invention, it can be confirmed that the nano particles are
consecutively uniformly coated on the carbon nano tube. Therefore,
the agglomeration phenomenon between the carbon nano tube particles
may be prevented. The agglomeration of the nano particles caused by
being entangled with other particles and wound thereto and the
agglomeration of the nano particles caused by surface tension such
as van der Waals forces between molecules at an nm level can be
prevented. Therefore, it may help in forming 3-dimensional network
architecture capable of improving mechanical strength or conductive
characteristics and a 3-dimensional porous structure.
[0062] In addition, the basic structure of the lithium manganese
oxide has a lithium manganese oxide-spinel
(LiMn.sub.2O.sub.4-Spinel) structure. The lithium ion has a lattice
structure capable of being three-dimensionally diffused by having
the spinel structure, such that the carbon nano composite according
to the present invention is advantageous in facilitating the
separation/insertion of the lithium ion as compared to other
lithium manganese oxides, thereby achieving the high-output
characteristics.
[0063] The electrode material has a 3-dimensional porous structure
due to the spinel structure of the lithium manganese oxide by
forming the lithium manganese oxide-carbon nano composite and the
diffusion rate of the lithium ion is increased, thereby making it
possible to maximize the electrochemical utility of the electrode
material. Further, most of the lithium manganese oxide-carbon nano
composite manufactured according to the present invention can
contribute to the specific capacitance even in the high-output
conditions and improve the electric conductivity of the carbon nano
composite, by coating the lithium manganese oxide at a thickness of
several nm by the chemical method. Therefore, the lithium manganese
oxide-carbon nano composite may be used as the high-capacity,
high-output electrode material.
[0064] FIG. 2 is a graph showing absorbance according to a waveform
of a synthesis solution before and after the manganese ion solution
according to the present invention is heat-treated in the
water.
[0065] Referring to FIG. 2, FIG. 2 shows the amount of manganese
ion existing in the mixing solution before/after the mixing
solution of the lithium ion solution and the manganese ion solution
is heat-treated. The exemplary embodiment of the present invention
use potassium permanganate (KMnO.sub.4) as the manganese ion
solution. Since the manganese ion is included in the mixing
solution before the manganese ion solution and the lithium ion
solution are heat-treated, an absorbed peak corresponding to the
waveform of the manganese ion is shown.
[0066] However, it can be confirmed that the peak is not shown at
the absorption wavelength of manganese ion after the manganese ion
is heat-treated at a temperature of between 120.degree. C. and
200.degree. C. It can be confirmed that the manganese ion is
reduced to LiMn.sub.2O.sub.4 nano particles on the carbon nano
composite by the heat treatment.
[0067] The related art requires a great deal of reaction time and
energy to synthesize the LiMn.sub.2O.sub.4. However, the microwave
is applied to the manganese ion solution and the lithium ion
solution to heat, thereby making it possible to very rapidly and
simply synthesize the LiMn.sub.2O.sub.4 nano particles.
[0068] FIG. 3 is a graph showing a cyclic voltammogram before and
after the lithium manganese oxide-carbon nano composite according
to the present invention is heat-treated in the water.
[0069] The oxide having the spinel structure has a crystal
structure of an isometric system and has excellent magnetism or
electrical conductivity.
[0070] If the LiMn.sub.2O.sub.4 nano particles have the spinel
structure, the current peak is shown at the cyclic voltammogram. It
can be appreciated from FIG. 3 that two current peaks are shown,
since the current peak showing the spinel structure is not observed
at the carbon nano composite before the heat treatment in the water
but the spinel structure of the LiMn.sub.2O.sub.4 nano particles
are formed on the carbon nano composite after the heat treatment in
the water.
[0071] Further, it can be appreciated that Li and Mn are accurately
formed at a tetrahedral place and an octahedral place on the spinel
structure without position confusion through a first current peak
in the vicinity of 4V and a second current peak in the vicinity of
4.2V among two peaks at the cyclic voltammogram of the lithium
manganese oxide-carbon nano composite after the heat-treatment in
the water.
[0072] FIG. 4 is a graph showing a constant current charge and
discharge profile before and after the lithium manganese
oxide-carbon nano composite according to the present invention is
heat-treated in the water.
[0073] When the particles have the spinel structure, a potential
plateau is found in the constant current charge and discharge
profile. This makes it easy to separate/insert the lithium ions by
allowing the carbon composite to have the spinel structure to
improve the output characteristics, such that the potential plateau
is found in the constant current charge and discharge profile.
[0074] Referring to FIG. 4, in the mixing solution including the
carbon material that is not subjected to the heat treatment in the
water, the potential plateau is not found in the constant current
charge and discharge profile; however, the potential plateau is
found within the constant current charge and discharge profile,
since the lithium manganese oxide-carbon nano composite is formed
after the heat treatment in the water. Therefore, it can be
appreciated that the LiMn.sub.2O.sub.4 nano particles have the
spinel structure after the heat treatment in the water.
[0075] As described above, when the LiMn.sub.2O.sub.4 nano
particles have the spinel structure, they have the lattice
structure capable of three-dimensionally diffusing the lithium ion,
such that they can easily separate and insert the lithium ions as
compared to other lithium manganese oxides, thereby having
high-output characteristics.
[0076] FIG. 5 is a graph showing a discharge curve for each C-rate
of the lithium manganese oxide-carbon nano composite according to
the present invention.
[0077] The current values of the charging or discharging are
represented by 1C, 2C, or the like. For example, if it is assumed
that there is a rechargeable battery having a capacity of 1000 mAh,
the 1C charging (or discharging, in this case, the charging and
discharging ends within 1 hour) is conducted when the rechargeable
battery is charged (or discharged) with a current of 1000 mAh. When
the rechargeable battery is charged (discharged) with a current
value of 2000 mAh, the 2C charging (or discharging, in this case,
the charging and discharging ends within 30 minutes). As described
above, the case in which the battery capacity is completely charged
or discharged within the predetermined time will now be described
based on a concept referred to as a C-rate. That is, the battery
capacity is defined by the current capacity rate per hour.
[0078] Referring to FIG. 5, it can be appreciated that the
discharge characteristics per the C-rate of the lithium manganese
oxide-carbon nano composite is finally synthesized by the heat
treatment in the water. It can be appreciated that the voltage
dropping width is gradually increased with the increase of the
C-rate. However, since the voltage drop is small even in the high
C-rate value, it can be appreciated that the electrode including
the lithium manganese oxide-carbon nano composite has a very low
ESR value.
[0079] FIG. 6 is a graph showing the C-rate dependency of the
specific capacitance of the lithium manganese oxide-carbon nano
composite according to the present invention.
[0080] FIG. 6 shows that the specific capacitances at 10, 20, and
50C-rates are compared under the assumption that the specific
capacitance demonstrated at the 1C rate is 100%.
[0081] In the lithium manganese oxide-carbon nano composite, it can
be appreciated that the specific capacitance is reduced with the
increase of the C-rate value and the specific capacitance of 100%
is maintained up to the 5C rate. Further, it can be appreciated
that the specific capacitance of 90% is maintained even at a very
fast discharge rate of the 20C rate.
[0082] It can be appreciated from FIGS. 9 and 10 that the lithium
manganese oxide-carbon nano composite has the very excellent
high-rate discharge characteristics. The reason is that the
diffusion length of the Li ion is reduced with the nanotization of
the LiMn.sub.2O.sub.4 and the LiMn.sub.2O.sub.4 is uniformly coated
on the carbon nano composite. Further, since the effective
interfacial area between the electrolyte and the LiMn.sub.2O.sub.4
is increased and the accessibility of the Li ion is increased due
to the porous structure between the carbon nano composites, it can
be appreciated that the discharge characteristics of the electrode
are improved when the lithium manganese oxide-carbon nano composite
is used as the electrode.
[0083] FIG. 7 is a flowchart showing lifespan characteristics of
the lithium manganese oxide-carbon nano composite according to the
present invention.
[0084] Referring to FIG. 7, the life characteristics of the energy
storage device when the lithium manganese oxide-carbon nano
composite is used as the electrode material can be appreciated. It
can be appreciated that the specific capacitance value is slightly
reduced even when the charging and discharging is continued at a
very fast rate of the 20C rate. It can be appreciated that the
specific capacitance value of 99.5% of the initial capacity is
maintained even when the charging and discharging are made 50 times
and the specific capacitance value of 96.5% is maintained even when
the charging and discharging are made 100 times.
[0085] Therefore, the lithium manganese oxide-carbon nano composite
according to the present invention can manufacture the high-output
energy storage device having the excellent high rate discharge
characteristics and the excellent lifespan characteristics.
Example
[0086] In order to synthesize the lithium manganese oxide-carbon
nano composite in which the LiMn.sub.2O.sub.4 nano particles were
dispersed, the microwave hydrothermal process was used.
[0087] In order to synthesize the lithium manganese oxide-carbon
nano composite, 0.1M of a KMnO.sub.4 aqueous solution and 1M of a
LiOH aqueous solution were first mixed at the same volume and were
agitated for 24 hours at normal temperature (S10).
[0088] After the mixing solution was put into the microwave
hydrothermal reacting container and the carbon nano composite was
added thereto (S20), the process of coating the carbon nano
composite with the lithium manganese oxide was performed for 1 hour
at 120.degree. C., until the reaction was completely finished
(S30). The prepared reaction products were withdrawn by centrifugal
separation and then washed with distilled water several times in
order to completely remove the ions remaining in the solution, and
were dried for 24 hours in an oven of 100.degree. C.
[0089] In order to control the composition of Li and Mn in the
synthesized powder, after the carbon nano composite coated with the
lithium manganese oxide was put in the microwave water heat
treatment reaction container and the distilled water was put
therein, the water heat treatment was performed for 1 hour at
200.degree. C.
[0090] In order to completely remove the adsorption water, the
synthesized powders were dried for 24 hours at 120.degree. C. in a
vacuum state.
[0091] Slurry in which the lithium manganese oxide-carbon nano
composite, a conductive material, and a binder were mixed at a
ratio of 67:28:5 was prepared in order to use the lithium manganese
oxide-carbon nano composite as the electrode material.
[0092] In this case, acetylene black was used as the conductive
material and PVDF dissolved with N-Methyl-2-Pyrrolidone (NMP) was
used as the binder. After the conductive material was added to the
lithium manganese oxide-carbon nano composite powder and they were
uniformly mixed by a ball mill, the binder and the NMP were added
thereto and they were uniformly mixed again by the ball mill.
[0093] The uniform slurry prepared by the method was applied to a
titanium foil current collector to manufacture the electrode, which
was then dried for 12 hours in an oven of 100.degree. C.
[0094] As set forth above, the present invention provides the
method for manufacturing a lithium manganese oxide-carbon nano
composite by mixing a lithium ion solution and a manganese ion
solution, dispersing a carbon material in the mixing solution of
the lithium ions and the manganese ions, maintaining the solution,
in which the carbon material is dispersed, at a predetermined
temperature, and coating the surface of the carbon material with
the lithium manganese oxide.
[0095] In addition, the present invention provides the lithium
manganese oxide-carbon nano composite in which the carbon material
is coated with the lithium manganese oxide at a thickness of
several nm.
[0096] Further, the present invention provides the manufacturing
apparatus capable of coating the carbon material with the lithium
manganese oxide at a thickness of several nm.
[0097] While the present invention has been shown and described in
connection with the exemplary embodiments, it will be apparent to
those skilled in the art that modifications and variations can be
made without departing from the spirit and scope of the invention
as defined by the appended claims.
* * * * *